Nickel plating



Patented Dec. 2 9 1953 2,664,392 NICKEL PLATING Newell F. Blackburn,

sylvania 7 Fort Belvoir, Va., assignor to The Pennsylvania SaltManufacturing Com-- puny; Philadelphia, Pa., a corporation of Penn.-

N Drawing. Application November 23', 1949,

Serial No.

9"Clain1s'. (01. 204-49).

This invention relatesto' nickel plating and more particularly to thedepositing. of bright nickel coatings on various types ofmetals' such assteel, copper, brass; etc- In the electro-depositing of nickel directlyon base metals various types of electrolyte 'baths have heretofore beenused, the most common of these being baths of the Niso4NiC12 type. Inmost of these baths, however, considerable difficulty has been.encountered due to metallic impurities, such, for example, as chromium,coppeigand zinc, interfering with the nickel deposit so as to produce adull or off-color plating. This is particularly objectionable where abright nickel deposit is desired. Another objection to baths oftheNiSO4--NiClz type is that there is considerable sludge formation atthe nickel anode. A build-up of sludge increases the resistan'ceat' theanode surface reducing the current for a given, voltage. Tocompensatefor this; more anode area is needed to reduce the.

totalanode resistance and thus'obt'ain'an equivalent nickel deposit,other factors being equal, to that which would be obtained if there wereno substantialamountof' sludge formation. The

large amount of sludge'formed is also wasteful of nickel and isdifii'cult to keep out of the main body of theelectrolyte where itspresenceacts as an impurity which affects deleteriously the nickeldeposit being" obtained.

After considerable experimentation with various types ofplating baths,it was noted that a plating bath of thenickel fluoborate type wasconsiderably superior to'the conventional plating baths in manyrespects. The nickel fluoborate baths were found to have asubstantiallyhigher' tolerance for metallic impurities, such aschromium, copper; zinc, etc., than the conventional nickel platingbaths. The formation of anode sludge, with the resulting objectionableeffects, was also considerably reduced providing a substantial saving incell operation. Besides these advantages over the conventionalNiSO4-NiClz plating baths, the use of nickel fluoborate baths timerequired. with the nickel fluoborate bath being, only about two-thirdsof that required. when using baths ofthe conventional nickelchloride-nickel sulfate type. Also, the fiuoboratesalts themselvesareideal buffers. Due to this,.

nickel. platingebaths, containing. no other buffer than the fiuoborateradical, maintain a constant pH during operation to a far greater degreethan the conventional NisO4NiC12 type baths.

These advantages, obtained by the use of the nickel fluoborate baths,naturally made the use of this bath preferable to those of theconventional type. However, where bright nickeldeposits were desired,the nickel fiuoborate bath alone was found to be unsatisfactory.

In order to obtain. bright nickel deposits from fiuoborate platingbaths, numerous conventional brightening agents were tried. These tendedto improve the brightness of the plating to alimited extent but did notgive a satisfactory brightness or the desired combination of brightnessand ductility which was deemed desirable. After trying numerous additionagents, both conventional brighteners and others, I have found thatif asmall percentage of sulfurized quinoidine (a product obtainedbysulfurizingthe mother liquor of cinchona bark after extraction of themedicinal alkaloids therefrom as described in the patent to Lutz, No.1,908,773 of May 16,

1933) is added to the bath, together with a small amount of benzoicsulfimide, an excellent bright deposit of nickel is obtained. The nickeldeposit obtained when using small amounts of sulfurized quinoidine andbenzoic-sulfimide had a bright, lustrous appearance. and did not havethe objectionable brittleness so often found in bright nickel depositsobtained by the use of many conventional brighteners. The deposits alsoshowed a satisfactory adherence to the metals on which they were plated.

In carrying out my invention I have found that the addition of 1- to 4grams per liter of benzoic sulfimide together with .01 to .03 gram perliter of sulfurized quinoidine to any nickel fluoborate electroplatingbath would produce considerably better bright nickel deposits thanobtained by use of these baths without the adbenzoic sulfimide isapproximately 1.5 to 2.3 grams benzoic sulfimide per liter ofelectrolyte. In preparing nickel fluoborate baths to be used with theabove ingredients, it was found advisable to keep the concentration ofnickel and fluoborate, bothv ionized and unionized, at above 1 3 gramsper liter of nickel and 37 grains per liter of fiuoborate theconcentration of'these materials generally being maintained within therange of 13 to gramsnickel and 37 to 230 grams BR; radical per liter ofelectrolyte. It is understood that the concentration of nickel aridfluoborate mentioned above and in the appended 3 claims includes boththe dissociated and undissociated nickel and fluoborate dissolved in thebath.

The addition of other materials, though not absolutely necessary for thepurpose of obtaining a bright nickel deposit, was found to improve theover-all operation of the bath. Among these materials might be mentionedboric acid which helps to prevent the formation of free hydrofluoricacid and tends to increase the life of the plating bath, the amountadded being preferably not less than 1 gram per liter, the maximumamount being limited by its solubility in the electrolyte though it isgenerally preferred not to use over 45 grams boric acid per liter ofelectrolyte; sodium and ammonium fluoborate, which tend to improve theconductivity of the bath, may be added in amounts ranging from none atall up to approximately 30 grams per liter of electrolyte it beinggenerally preferred not to exceed the 30 grams per liter; and a smallamount of wetting agent such, for example, as sodium lauryl sulfate oran alkyl aryl sulfonate, the purpose of the wetting agent beingprimarily to reduce pitting in the nickel deposit and to produce a moreuniform bright deposit, the amount of such wetting agent beingpreferably about to 15 grams per 100 gallons of electrolyte. W

Even though the fluoborate baths are extremely tolerant of solubleimpurities they are somewhat sensitive to insoluble impurities andfloating particles. Therefore, in order to obtain the best results it ispreferred to use regular cast nickel anodes of good purity.

The nickel fluoborate, which appears to be the active plating ingredientin this type of bath, may be formed by several methods such, forexample, as by reacting fluoboric acid and a nickel salt; an inert metalfluoride; a nickel salt and boric acid; a nickel salt, hydrogen fluorideand boric acid; nickel fluoride and boric acid; or by the reaction ofother water-soluble compounds which would produce as a reaction productthe nickel fluoborate. The nickel and fluoborate radicals are generallyadded together as nickel fluoborate. Preferred baths, for example, Wouldgenerally contain 80 to 110 grams per liter of nickel fluoborate, 25 to35 grams per liter of boric acid, 1.5 to 2.3 grams per liter of benzoicsulflmide and .01 to .03 gram per liter of sulfurized quinoidine. Toobtain the best results the pH of the bath is preferably maintained atbetween 2.5 and 5.5 the preferred pH being approximately 3 to 4. Thismay be done by the addition of such materials as fluoboric acid ornickel carbonate. It is also desirable to maintain the temperature whenusing the bath somewhere in the range of 40 to 80 C. the best resultsbeing obtained with temperatures of 45 to 65 C. Cathode currentdensities of between 15 to 100 amperes per square foot of active cathodesurface are generally employed.

The following are a few specific formulations of bright nickelelectroplating baths together with operating conditions. These are givenby way of example only for the purpose of better illustrating theinvention and should not be considered in any way as limiting the same.

E ramble 1 Ni(BF4)2 100 grams per liter H3303 30 grams per liter Benzoicsulfimide 1 gram per liter sulfurized quinoidine .05 gram per gallonTemperature 65 C.

Cathode current density up to 50 amperes per square foot Anode currentdensity 50 amperes per square foot Example 2 Ni(BF4) z 200 grams perliter HsBOs 30 grams per liter Benzoic sulfimide 2 grams per litersulfurized quinoidine .05 gram per gallon Temperature 65 C.

Cathode current density up to amperes per square foot Anode currentdensity 50 amperes per square foot Example 3 A 100 gallon bright nickelplating bath was prepared by mixing 20 gallons of 50% nickel fluoboratesolution (weight to volume, equal to 88 lbs. nickel fluoborate) with 60gallons of water. In this bath were dissolved 12.5 lbs. of boric acid,ounce of a wetting agent of the alkyl aryl sulfonate type, 10 ounces ofbenzoic sulfimide and 0.1 ounce of sulfurized quinoidine. After theaddition of these materials the volume of the bath was adjusted to 100gallons and the pH adjusted, either by the addition of nickel carbonateor fluoboric acid to a pH range of 3.5 to 4.5.

Several platings were made from this bath during which the temperatureof the bath was varied from to F. while the cathode current density wasvaried from 20 to 80 amperes per square foot. An anode current densityof about 50 amperes per square foot was used throughout the platingoperations. The result in each instance was a bright and uniform nickeldeposit.

In each of the above examples satisfactory bright nickel deposits wereobtained. These deposits Were found to have good ductility and showed astrong adherence to the base metals to which they were plated.

In describing the invention, specific examples have been given. However,it is apparent that various modifications of the electrolytic bath, bothin percentage of ingredients and by the addition of other ingredients tothe bath may be made without departing from the scope of the invention.

Having thus described my invention, I claim:

1. A method for electro-depositing bright ductile deposits of nickelwhich comprises electrolyzing an aqueous solution of nickel fluoboratehaving small quantities of sulfurized quinoidine and benzoic sulfimidetherein sufficient to produce bright nickel deposits from said solution.

2. A method for electro-depositing bright ductile deposits of nickelwhich comprises electrolyzing an aqueous solution of nickel fluoboratehaving .01 to .03 gram per liter of sulfurized quinoidine and 1 to 4grams per liter of benzoic sulfimide therein.

3. An electrolyte for depositing bright nickel coatings comprising awater solution containing not less than 13 grams per liter of nickel,not less than 37 grams per liter of BF4 radical, 1 to 4 grams per literof benzoic sulfimide and .01 to .03 gram per liter of sulfurizedquinoidine.

4. An electrolyte for depositing bright ductile nickel coatingscomprising a water solution containing not less than 13 grams per literof nickel, not less than 37 grams per liter of HE; radical, 1 to 45grams per liter of boric acid, 0 to 30 grams per liter of ammoniumfluoborate, 1 to 4 grams per liter of benzoic sulfimide and .01 to .03gram per liter of sulfurized quinoidine.

5. An electrolyte for depositing bright ductile nickel coatingscomprising a water solution containing 13 to 80 grams of nickel perliter of electrolyte, 37 to 230 grams of BF4 radical per liter ofelectrolyte fluoborate, not less than 1 gram of boric acid per liter ofelectrolyte, and a small amount of brightening agents consist ing of 1to 4 grams per liter of benzoic sulfimide and .01 to .03 gram per literof sulfurized quincidene, the pH of said electrolyte being between 2.5and 5.5.

6. A method of electro-depositing bright ductile nickel deposits whichcomprises electrolyzing a water solution of nickel fiuoborate having 1to 4 grams per liter of benzoic sulfimide and .01 to .03 gram per literof sulfurized quinoidine at a temperature of between 40 and 80 C. and acathode current density of between 15 and 100 amperes per square foot,the pH of said electrolyte being maintained between 2.5 and 5.5

7. A method for electro-depositing bright ductile nickel deposits whichcomprises electrolyzing a water solution having therein 13 to 80 gramsper liter of nickel, 37 to 230 grams per liter of BE; radical, 1 tograms per liter of boric acid, 1 to 4 grams per liter of benzoicsulfimide and .01 to .03 gram per liter of sulfurized quinoidine at atemperature of 45 to C., the pH of said electrolyte being maintainedbetween 3 and 4.

8. An electrolyte for depositing bright ductile nickel coatingscomprising a water solution of substantially 13 to grams per liter ofnickel, 37 to 230 grams per liter of BF4 radical, not less than 1 gramper liter of boric acid, 1 to 4 grams per liter of benzoic sulfimide,.01 to .08 gram per liter of sulfurized quinoidine, and a salt selectedfrom the group sodium fiuoborate and ammonium fluoborate the amount ofsaid salt being not over 30 grams per liter.

9. The electrolyte of claim 5 to which has been added 5 to 15 grams of awetting'agent for each gallons of electrolyte.

NEWELL F. BLACKBURN.

References Cited in the file of this patent UNITED STATES PATENTS

1. A METHOD FOR ELECTRO-DEPOSITING BRIGHT DUCTILE DEPOSITS OF NICKELWHICH COMPRISES ELECTROLYZING AN AQUEOUS SOLUTION OF NICKEL FLUOBORATEHAVING SMALL QUANTITIES OF SULFURIZED QUINOIDINE AND BENZOIC SULFIMIDETHEREIN SUFFICIENT TO PRODUCE BRIGHT NICKEL DEPOSITS FROM SAID SOLUTION.